get_etog_matrix

gdt.missions.fermi.gbm.localization.dol.legacy_functions.get_etog_matrix()[source]

Function to calculate equatorial (ra, dec) to Galactic (lii, bii) coordinate rotation matrix.

Returns:

  • etog (np.ndarray((3,3), float64)) – Rotation matrix for transforming equatorial to galactic vectors

  • Version V1.0

  • This subroutine creates the 3x3 matrix that converts 1950 equatorial

  • coordinates into galactic coordinates lii and bii.

  • This subroutine is called by EQ1950_TO_GAL and by EQ2000_TO_GAL.

  • Michael S. Briggs, 16 July 1992, UAH / MSFC ES-62.

  • The transformation is based upon the following, which is the definition

  • of the galatic coordinate system – Location RA 1950 DEC 1950

  • North Galatic Pole 12h49m = 192.25 deg +27d24’ = +27.4 deg – Galactic Origin 17h42.4m = 265.6 deg -28d55’ = -28.9166666..

  • Also the ascending node of the galactic plane on the celestial equator

  • is lii = 33.0 degrees. All the above numbers are exact by definition

  • in 1950 coordinates.

  • See

  • 1) Practical Astronomy with your Calculator, 3rd ed., –

    1. Duffett-Smith, p. 43 & 50.

  • 2) Astrophysical Formulae, 2nd ed., K. R. Lang, p. 498 & 504.

  • 3) Third Reference Catalogue of Bright Galaxies, vol. 1, p. 11.

  • 4) Astronomical Algorithms, J. Meeus, p. 89 & 90.

  • Verification of this subroutine

  • The matrix calculated by this subroutine is a higher precision version

  • of the matrix given on page 50 of Practical Astron. with your Calculator.

  • The numbers in the matrix in that book agree with those calculated

  • by this subroutine to +/-1 on the last digit.